The process of removing hydrocarbon-based oily soils from industrial garments is well known. Surfactants are used as a means to remove hydrocarbon based oil, lowering the surface tension at the fabric/soil-water interface and creating an emulsion as the oily soils are lifted from the fabric and suspended in the wash liquor until it can be drained from the wash load. Typically, the surfactant wash process is done under alkaline conditions. A person skilled in the art of developing industrial laundry detergents understands the need and function of surfactants, soils suspending agents, water conditioners and alkali in the successful removal of oily industrial soils. In some cases, though, the oily soil contains a metallic component that is not readily removed via the emulsification process. These types of soils result in residual stains or soils that remain on the garment after being processed.
To resolve this, a pre-wash step has been employed that uses oxalic acid to change the valence of the metal to make it more water soluble. This treatment is generally followed by the normal washing process. Oxalic acid is a moderately strong carboxylic acid with a pKa1=1.27 and pKa2=4.27. Unfortunately, the oxalic acid is a powder and has relatively limited solubility in water (<15 g/100 mL). Therefore, it is impossible to obtain a highly concentrated solution of oxalic acid that is cost effective for dispensing by automatic equipment. As most industrial laundries rely on the accuracy and safety of automatic chemical dispensing equipment, the oxalic acid pre-wash is unsuitable for many laundering facilities. Identifying a compound that is a concentrated (>50%) liquid and can provide the same result as oxalic acid is most desired. Unfortunately, oxalic acid is the only known acid which effectively treats these oily metallic soils.